Your boyfriend's increased ticklishness, as a result of weight loss is something that I can certainly relate to, anonymiss86, since the sensitivity to touch of my stomach, ribs and sides increase considerably when I embark upon a period of cutting (a downside to maintaining an athletic physique).
While my stomach and ribs have always been incredibly susceptible to tickling, when dropping body fat, the areas seemingly become more so. As such, my non-ticklish partner thoroughly enjoys conducting the 'tickle test' during my period of cutting, by regularly raking her fingernails lightly over the skin of my upper torso to see how much I react. In the absence of a set of calipers (to measure existing body fat), long finger nails testing ticklish skin is another reliable way of assessing the reduction of body fat.
My theory, as to why ticklishness in some may increase through weight loss, rests upon the fact that a reduction in subcutaneous fat directly beneath the skin's surface means there's less fat covering the nerve endings. As such, the lack of insulation leaves the nerve endings better able to feel the stimulus applied. Through the increased energy generated (as nerves bounce off one another, sending signals back to the brain), a more profound reaction on the part of a ticklee ensues.
Just as much as weight loss and exercise can improve the sensitivity of hormones, such as insulin, I believe it can also have a profound effect upon some of us who happen to be ticklish.
